io.permazen

Class SnapshotJTransaction

java.lang.Object

io.permazen.JTransaction

io.permazen.SnapshotJTransaction

All Implemented Interfaces:

Closeable, AutoCloseable

public class SnapshotJTransaction
extends JTransaction
implements Closeable

An in-memory JTransaction that persists indefinitely.

The purpose of SnapshotJTransactions is to hold a "snapshot" some portion of the state of a parent JTransaction for later use after the parent transaction closes. Each SnapshotJTransaction contains its own set of "snapshot" JObjects that are (usually) copies of the corresponding "real" database JObjects. A SnapshotJTransaction has the same schema as its parent JTransaction.

For convenience, each JTransaction has a default SnapshotJTransaction instance associated with it; JObject.copyOut() copies objects there.

Because SnapshotJTransactions live indefinitely, their objects can be used just like normal Java objects, outside of any regular transaction, yet all of the usual Permazen features such as indexing, listeners, validation, etc., continue to function normally.

Other Uses

More general usage beyond snapshots of regular transactions is possible: an empty SnapshotJTransaction can be created on the fly via JTransaction.createSnapshotTransaction() and then used as simple in-memory transaction "workspace". The resulting key/value pairs could then be (de)serialized and sent over the network; see for example JObjectHttpMessageConverter.

For KVDatabase's that support it, using the key/value store snapshot returned by KVTransaction.mutableSnapshot() allows an efficient "copy" of the entire database into a SnapshotJTransaction using Permazen.createSnapshotTransaction().

See Also:

Transaction.createSnapshotTransaction(), Permazen.createSnapshotTransaction(), SnapshotTransaction

Method Summary

Modifier and Type	Method and Description
void	close() Close this instance and release any resources associated with it.
void	commit() Commit this transaction.
SnapshotTransaction	getTransaction() Get the SnapshotTransaction associated with this instance.
boolean	isSnapshot() Determine whether this instance is a SnapshotJTransaction.
boolean	isValid() Determine whether this transaction is still valid.
void	reset() Delete all objects contained in this snapshot transaction and reset it back to its initial state.
void	rollback() Roll back this transaction.

Methods inherited from class io.permazen.JTransaction

cascadeFindAll, cascadeFindAll, copyTo, copyTo, copyTo, copyTo, create, create, createClones, createSnapshotTransaction, delete, exists, followReferencePath, get, get, get, getAll, getCurrent, getKey, getKey, getPermazen, getSchemaVersion, getSnapshotTransaction, getValidationMode, invertReferencePath, performAction, queryCompositeIndex, queryCompositeIndex, queryCompositeIndex, queryIndex, queryIndex, queryListElementIndex, queryMapValueIndex, queryVersion, readCounterField, readListField, readMapField, readSetField, readSimpleField, recreate, registerJObject, resetValidationQueue, revalidate, setCurrent, updateSchemaVersion, validate, weakConsistency, writeSimpleField

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

isSnapshot

public boolean isSnapshot()

Description copied from class: JTransaction

Determine whether this instance is a SnapshotJTransaction.

Overrides:

isSnapshot in class JTransaction

Returns:

true if this instance is a SnapshotJTransaction, otherwise false

getTransaction

public SnapshotTransaction getTransaction()

Get the SnapshotTransaction associated with this instance.

Overrides:

getTransaction in class JTransaction

Returns:

the associated core API snapshot transaction

reset

public void reset()

Delete all objects contained in this snapshot transaction and reset it back to its initial state.

It will contain schema meta-data but no objects.

commit

public void commit()

Commit this transaction.

SnapshotJTransactions do not support this method and will always throw UnsupportedOperationException.

Overrides:

commit in class JTransaction

Throws:

UnsupportedOperationException - always

rollback

public void rollback()

Roll back this transaction.

SnapshotJTransactions do not support this method and will always throw UnsupportedOperationException.

Overrides:

rollback in class JTransaction

Throws:

UnsupportedOperationException - always

isValid

public boolean isValid()

Determine whether this transaction is still valid.

SnapshotJTransactions are always valid.

Overrides:

isValid in class JTransaction

Returns:

true always

See Also:

Transaction.isValid()

close

public void close()

Close this instance and release any resources associated with it.

The implementation in SnapshotJTransactions closes the underlying SnapshotTransaction.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

See Also:

SnapshotTransaction.close()